Recent years, in response to the needs for electronic devices such as miniaturization, speeding up, integration, and multifunctionality, the manufacture of devices containing functional materials such as electronic ceramics, which express predetermined functions by being applied with electric fields or magnetic fields and include a dielectric material, piezoelectric material, magnetic material, pyroelectric material and semiconductor material, by using various film formation technologies has been actively studied.
For example, in order to enable high-definition and high-quality printing in an inkjet printer, it is necessary to miniaturize and highly integrate ink nozzles of inkjet heads. Accordingly, it is also necessary to similarly miniaturize and highly integrate piezoelectric actuators for driving the respective ink nozzles. In such a case, a film formation technology, that enables formation of a thinner layer than a bulk material and formation of fine patterns, is desired, and film formation technologies such as a sputtering method, a sol-gel method, and an aerosol deposition method have been studied.
However, there has been a problem that a film of function material (also simply referred to as “functional film”) formed by film formation does not sufficiently exert its function in a condition after the film formation, and the film is inferior to a bulk material in performance.
In order to sufficiently express the function of a functional film, heat treatment at relatively high temperature (e.g., about 500° C. to 1000° C.) is required after film formation. Since a substrate that is used at the time of film formation (film formation substrate) is simultaneously heat-treated, high heat tolerance is required for the material of film formation substrate. On the other hand, in the case where a fabricated function film is utilized, there is demand for using various kinds of substrates according to instruments such as a flexibly substrate made of resin, for example. Accordingly, a method has been studied by which a functional film formed on a film formation substrate can be peeled or transferred from the film formation substrate without hindering its function.
As a related technology, Japanese Patent Application Publication JP-A-54-94905 discloses a multilayered structure for thin film transfer having a heat-resistant substrate, a release layer principally containing carbon and/or carbon compound, and a functional thin film as main component elements (page 1). Further, JP-A-54-94905 discloses that the functional thin film can be peeled from the heat-resistant substrate and transferred to another substrate because the release layer can be removed by oxidization (combustion) (page 3).
Japanese Patent Application Publication JP-A-10-125929 discloses a peeling method by which any material to be peeled can be easily peeled regardless of its properties and conditions, and especially, the peeled material can be transferred to various transfer materials. The peeling method is to peel a material to be peeled existing on a substrate via a separation layer having a multilayered structure of plural layers from the substrate, and includes the steps of applying irradiating light to the separation layer to cause peeling within the layer of the separation layer and/or at an interface thereof so as to detach the material to be peeled from the substrate (pages 1 and 2). Further, in JP-A-10-125929, as the composition of a light absorption layer, amorphous silicon, silicon oxide, dielectric material, nitride ceramics, organic polymer and so on are cited (pages 5 and 6).
Japanese Patent Application Publication JP-P2004-165679A discloses a method of transferring a layer to be transferred containing a thin film device to a secondary transfer material, which method is for matching (i) a multilayer relationship of the layer to be transferred against a substrate used when the layer to be transferred is manufactured and (ii) a multilayer relationship of the layer to be transferred against a transfer material as a transfer destination of the layer to be transferred. The method includes the first step of forming a first separation layer on a substrate, the second step of forming a layer to be transferred containing a thin film device on the first separation layer, the third step of forming a second separation layer consisting of a water-soluble or organic solvent-soluble adhesive agent on the layer to be transferred, the fourth step of bonding a primary transfer material onto the second separation layer, the fifth step of removing the substrate from a material to be transferred by using the first separation layer as a boundary, the sixth step of bonding a secondary transfer material to an undersurface of the layer to be transferred, and the seventh step of bringing the second separation layer into contact with water or organic solvent to remove the primary transfer material from the transfer layer by using the second separation layer as a boundary (pages 1 and 2). Further, in JP-P2004-165679A, as the composition of the separation layer, amorphous silicon, silicon oxide, dielectric material, nitride ceramics, organic polymer and so on are cited (pages 8 and 9).
However, according to JP-A-54-94905, since the release layer is removed by oxidation reaction, the atmosphere in the heat treatment process is limited to an oxygen atmosphere. Further, since carbon or carbon compound is used as the release layer, there is the upper limit to heating temperature. For example, in an embodiment disclosed in JP-A-54-94905 (pages 1 and 3), the treatment temperature in the transfer process is 630° C. at the highest. Therefore, the invention disclosed in JP-A-54-94905 cannot be applied to a manufacture of electronic ceramics that requires heat treatment at relatively high temperature (e.g., 700° C. or more).
According to JP-A-10-125929, peeling is caused within the separation layer or at the interface by applying a laser beam to a light absorption layer contained in the separation layer to allow the light absorption layer to ablate. That is, a solid material contained in the light absorption layer is photochemically or thermally excited by absorbing applied light, and thereby, bonding between atoms or molecules of the surface or inside thereof is cut and they are released. As a result, a phase change such as melting or transpiration (vaporization) occurs in the constituent material of the light absorption layer, and the material to be peeled is peeled at relatively low temperature. However, according to the method, the peeling property is likely to be insufficient. Further, JP-A-10-125929 does not disclose that a chemical change such as reaction with other component or decomposition is made in a constituent material of the light absorption layer.
On the other hand, according to JP-P2004-165679A, when the thin film device is detached from the substrate by applying a laser beam to the separation layer, in order to peel the thin film device from the substrate more reliably, ions for promoting peeling are implanted into the separation layer. According to such a method, inner pressure is generated in the separation layer and the peeling phenomenon is promoted. However, since hydrogen ions cited as ions for promoting peeling in JP-P2004-165679A are gasified at 350° C. or more and exit from the separation layer (page 6), the process temperature after ion implantation can not be set to 350° C. or more.